Liquid crystal display device

ABSTRACT

In a liquid crystal display (LCD) device having a thin film transistor (TFT), the TFT includes a source electrode, a drain electrode and a semiconductor layer. At least one of the source electrode and drain electrode includes a first layer including copper and a second layer forming an oxide layer and covering the first layer. The semiconductor layer has a substantially linear current-voltage relationship with said source electrode or drain electrode including said first and second layers, when a voltage is applied between the semiconductor layer and said source electrode or drain electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/453,946 filed Apr. 23, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/583,165, filed Aug. 13, 2009, now U.S. Pat. No.8,164,701, issued Apr. 24, 2012, which claims priority under 35 U.S.C.§119 from Japanese Patent Application Serial No. 2008-210226, filed Aug.19, 2008, each of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to a liquid crystal display (LCD) devicehaving a thin film transistor (TFT).

BACKGROUND

In recent years, low-power-consumption liquid crystal display (LCD)devices, which are thin and light in terms of weight and may also bedriven with low value voltages, are widely used. In addition, the demandfor increasing the screen size is higher year after year, and motionpictures such as TV images are required to be displayed on thesedevices. For that, interconnections need to be composed of materialsthat have low resistivity and high conductivity. In recent years, inresponse to the above requirements interconnections are expected to bemade of new materials such as copper (Cu). Copper (Cu) has lowerresistivity, namely higher conductivity compared to aluminum (Al)alloys.

According to the actual demand for large screens, materials for gateinterconnections have changed from a molybdenum (Mo) alloy to analuminum (Al) alloy or an aluminum clad, etc. Needless to mention thatAluminum (Al) has problems of hillocks, migrations, etc.

For example, as shown in Japanese Unexamined Patent ApplicationPublication No. 2000-199054, interconnection materials composed of analuminum-neodymium (Al—Nd) alloy is proposed, or anodically oxidized Al,Al claded by molybdenum (Mo) alloy, or double layered aluminum (Al) isused. In the case of aluminum-neodymium (Al—Nd) alloy the resistivity ofinterconnections is about 5.1 μΩcm, while the resistivity of purealuminum (Al) is 2.5 μΩcm.

Therefore, interconnections composed of three layers oftitanium/aluminum/titanium (Ti/Al/Ti) or molybdenum/aluminum/molybdenum(Mo/Al/Mo) are used as a countermeasure against the above mentionedproblems of hillocks, migrations, etc. when pure aluminum (Al) ispractically used as a material for interconnections. However, thismultilayer structure brings about new problems such as an increase inthe layer formation process.

On the other hand, nowadays, copper (Cu) is considered to be anattractive material for thin film transistor (TFT) electrodes orinterconnections because it represents a low electrical resistancecompared to the other materials used in TFT electrodes orinterconnections. However, copper (Cu) has poor characteristics withregards to the adhesiveness with insulating layers, in particular, withglass, which is a material used for the substrate of TFT. In addition,copper (Cu) gets easily oxidized when formed on an insulating layer.

Accordingly, to resolve the above-mentioned problems, a techniqueemploying alloyed copper interconnections is attempted in TFT-LCDdevices. This technique aims at securing the adhesiveness to the glasssubstrate by reaction of alloy elements with the substrate forming alayer at their interface. In addition, this technique also aims atforming an oxide layer on a surface of copper (Cu), in which the alloyelements function as an oxidation-resistance layer with a lowresistivity for the copper (Cu).

However, according to the proposed technique, characteristics that areaimed at are not sufficiently achieved. Electric resistance of copper(Cu) increases due to the fact that alloy elements are remaining in Culayer, and therefore it could not show its advantage over conventionalinterconnection materials such as aluminum (Al) or aluminum alloy.

Further, as shown in Japanese Unexamined Patent Application PublicationNo. 2004-163901, in order to utilize a copper interconnection in TFT-LCDdevices, another technique is proposed in that a molybdenum (Mo) alloylayer is interposed between the copper (Cu) layer and the substrate,thereby securing the adhesiveness and the barrier properties with thesubstrate.

However, according to this technique, the manufacturing process has anadditional step for depositing molybdenum (Mo) alloy. In addition, theeffective resistance of interconnections increases in this structure.Further, although a single layer of copper (Cu) is utilized for thesource and drain electrodes of TFT-LCD devices, their stability remainsunder question.

Further, in Japanese Unexamined Patent Application Publication No.2004-139057, in order to resolve the above mentioned problems withregards to the copper (Cu) interconnections, another technique isproposed in that a high-melting-point nitride such as tantalum nitride(TaN), titanium nitride (TiN) or tungsten nitride (WN) is formed aroundthe copper (Cu). However, this technique arises other problems such as,for example, a new material for forming the barrier layer and even anadditional process are required compared to the case where conventionalmaterials are used for the interconnections. In addition, the effectiveresistance of the interconnection increases because a high-resistivitybarrier layer is deposited thickly around the copper (Cu).

Further, Japanese Unexamined Patent Application Publication No.2005-166757 discloses that an addition of one or more elements ofmagnesium (Mg), titanium (Ti) and chromium (Cr) to the copper (Cu) ofthe interconnections in TFT-LCD devices improves the adhesiveness aswell as the oxidation resistance. However, another problem arises inthat the interconnection resistance increases as the additional elementsare remaining in the interconnections. In addition, the interconnectionresistance increases because the additional elements reduce oxides inthe substrate layer and the reduced elements diffuse into theinterconnection.

Japanese Unexamined Patent Application Publication No. 2002-69550discloses another technique, which tries to improve the oxidationresistance by adding silver (Ag) of 0.3 to 10 weight percent to thecopper (Cu). However, in this case, the adhesiveness to the glasssubstrate is not improved, and sufficient oxidation resistance may notbe acquired to withstand liquid crystal manufacturing process.

Japanese Unexamined Patent Application Publication No. 2005-158887proposes a copper alloy in which at least one element of titanium (Ti),molybdenum (Mo), nickel (Ni), aluminum (Al) and silver (Ag) is added by0.5 to weight percent to the copper (Cu). However, the additionalelement increases electric resistance of the interconnections.

Japanese Unexamined Patent Application Publication No. 2004-91907discloses the addition of molybdenum (Mo) by 0.1 to 3.0 weight percentto the copper (Cu) and segregation of molybdenum (Mo) to a grainboundary suppresses oxidation by grain boundary diffusion. Although thistechnique can improve oxidation resistance of the copper (Cu), there isa problem in that the interconnection resistance increases.

International Unexamined Patent Application Publication No.WO2006-025347 discloses that an oxide protective layer formed by anadditional element will suppress the oxidation of Cu in the copper alloylayer in which the appropriate additional element is added. Theprotective layer is formed at an interface of an adjacent insulatinglayer that suppresses the mutual diffusion. This technique provides acopper interconnection that has high conductivity and good adhesivenesswith the substrate. Further, this technique provides liquid crystaldisplay (LCD) devices utilizing this copper interconnections. Inaddition, this publication suggests that manganese (Mn) is preferable asone of the additional elements. However, this technique is insufficientto realize features of interconnection structures used in the liquidcrystal display (LCD) devices and TFT electrode structures.

Japanese patent No. 3302894 proposes a TFT structure used in TFT-LCDdevices and explicitly discloses the gate electrode of TFT structure iscovered by an oxide layer when a Cu alloy is applied to the gateelectrode. This patent discloses that when a first metal is Cu, a secondmetal is at least one element selected from titanium (Ti), zirconium(Zr), hafnium (Hf), tantalum (Ta), niobium (Nb), silicon (Si), boron(B), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu),gadolinium (Gd), dysprosium (Dy), yttrium (Y), ytterbium (Yb), cerium(Ce), magnesium (Mg), thorium (Th), and chromium (Cr). However, thesecond element is different from an additional element of the presentinvention.

None of the above-mentioned documents refers to a structure of source ordrain electrodes in a TFT structure. However, high adhesiveness to asemiconductor layer or a pixel electrode, tolerability to a circumstancein which the TFT electrode is used, and stability of electric contactswith source or drain electrodes portion are required for the structureof the source or drain electrode. Therefore, the structure of the sourceor drain electrode is an important element of liquid crystal display(LCD) device.

As mentioned above, according to these conventional techniques, althoughadhesiveness to the semiconductor layer or the pixel electrode and theoxidation-resistance layer are tried to be secured by adding anadditional alloyed element to the copper (Cu), a sufficient result isnot yet obtained in all techniques. Further, sufficient results are notobtained with regard to the high adhesiveness to the semiconductor layeror the pixel electrode and tolerability of circumstances in which theTFT electrode is used. In the same way, the requirement of having stableelectric contacts with the source or drain electrodes portion are notyet met.

Especially, although the International Unexamined Patent ApplicationPublication No. WO2006-025347 suggests the liquid crystal display (LCD)device using copper interconnections, a sufficient structure forrealizing the gate interconnection structure utilized in the liquidcrystal display (LCD) device is not yet achieved by the suggestedtechnique. Further, the Japanese patent No. 3302894 clearly specifiesthat an oxide layer covering a gate electrode is an oxide layer mainlycomposed of a second metal element, which is formed by applying a heattreatment in an oxygen atmosphere. However, it is not described at allnor even suggested that the adhesiveness between the semiconductor layerand the source electrode or drain electrode is secured by forming anoxide layer on the source or drain electrodes as a result of reactionbetween Cu alloy and a Si oxide layer contacting to the Cu alloy by heattreatment, as mentioned in the present invention. Further, anelectrically stable contact between the source electrode or drainelectrode and the semiconductor layer is not described nor suggested.

In other words, there is a need to provide a solution for all theabove-mentioned problems such as, for example, depositing the Cu alloylayer with fewer process steps, decreasing effective resistance ofinterconnections, and forming a stable electric contact with improvingthe adhesiveness between the semiconductor layer and the source or drainelectrodes. However, these problems cannot be solved by theabove-mentioned conventional techniques, therefore actual products,featuring all the requirements, are difficult to be manufactured.

The present invention is made under the above-mentioned situation. Thepurpose of the present invention is to prevent an oxidation ofinterconnection materials, including a source electrode or drainelectrode, by forming an oxide layer covering the interconnections andsecuring a high adhesiveness to a semiconductor layer or a pixelelectrode. Further, the purpose of the present invention is to provide aliquid crystal display (LCD) device having a TFT structure in which asource electrode or drain electrode is sandwiched between thesemiconductor layer, such as amorphous silicon, and a passivation layerwith a stable ohmic contact.

SUMMARY

In accordance with a first aspect of the present invention, in a liquidcrystal display (LCD) device having a thin film transistor (TFT), theTFT includes:

a source electrode;

a drain electrode, where at least one of said source electrode and drainelectrode includes:

a first layer including copper, [0028] a second layer forming an oxidelayer and covering said first layer; and

a semiconductor layer having a substantially linear current-voltagerelationship with said source electrode or drain electrode includingsaid first and second layers, when a voltage is applied between thesemiconductor layer and said source electrode or drain electrode.

In the first aspect of the present invention described above, the secondlayer forming the oxide layer covers the first layer in the source ordrain electrode. Therefore, copper in the first layer is prevented fromoxidation. Further, the semiconductor layer has the substantially linearcurrent-voltage relationship with the source electrode or drainelectrode even though the oxide layer covers the first layer in thesource electrode or drain electrode. Such a substantially linearcurrent-voltage relationship is a preferable characteristic for a TFTtransistor of a LCD device.

In accordance with a second aspect of the present invention, in a liquidcrystal display (LCD) device having a thin film transistor (TFT), theTFT includes:

a source electrode;

a drain electrode, where at least one of said source electrode and drainelectrode includes:

a first layer including copper, [0035] a second layer forming an oxidelayer for sandwiching said first layer; and

a semiconductor layer having a substantially linear current-voltagerelationship with said source electrode or drain electrode with saidfirst and second layers, when a voltage is applied between thesemiconductor layer and said source electrode or drain electrode.

In the second aspect of the present invention described above, thesecond layer forming the oxide layer sandwiches the first layer in thesource or drain electrode. Therefore, copper in the first layer isprevented from oxidation. Further, the semiconductor layer has thesubstantially linear current-voltage relationship with the sourceelectrode or drain electrode even though the oxide layer sandwiches thefirst layer in the source electrode or drain electrode. Such asubstantially linear current-voltage relationship is a preferablecharacteristic for a TFT transistor of a LCD device.

In accordance with a third aspect of the present invention, in a liquidcrystal display (LCD) device having a thin film transistor (TFT), theTFT includes:

a source electrode;

a drain electrode, where at least one of said source electrode and drainelectrode includes:

a first layer including copper and manganese, [0042] a second layerforming an oxide layer including manganese and covering said firstlayer; and

a semiconductor layer having a substantially linear current-voltagerelationship with said source electrode or drain electrode with saidfirst and second layers, when a voltage is applied between thesemiconductor layer and said source electrode or drain electrode.

In the third aspect of the present invention described above, the secondlayer forming the oxide layer covers the first layer in the source ordrain electrode. Therefore, copper in the first layer is prevented fromoxidation. Further, the semiconductor layer has the substantially linearcurrent-voltage relationship with the source electrode or drainelectrode even though the oxide layer sandwiches the first layer in thesource electrode or drain electrode. Such a substantially linearcurrent-voltage relationship is a preferable characteristic for a TFTtransistor of a LCD device. Further, the second layer is an oxide layerincluding manganese. Therefore, adhesiveness between the sourceelectrode or drain electrode and the semiconductor layer is secured.Copper in the first layer is also prevented from diffusing into thesemiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a thin film transistorliquid crystal display (TFT-LCD) module.

FIG. 2 illustrates a cross-sectional view of a LCD display panel.

FIG. 3 is a conceptual view of an IPS liquid crystal display device.

FIG. 4 illustrates a plan view of a pixel portion and a TFT portion.

FIG. 5 illustrates a cross-sectional view of a pixel portion and a TFTportion.

FIG. 6 illustrates a schematic diagram of an equivalent circuit for apixel portion and a TFT portion.

FIG. 7 illustrates a schematic diagram of an embodiment of a TFTstructure (a top gate structure having a staggered type).

FIG. 8 illustrates a schematic diagram of an alternative embodiment of aTFT structure (a channel stopper structure having an inverted-staggeredtype).

FIG. 9 illustrates a schematic diagram of an alternative embodiment of aTFT structure (a channel etch structure having an inverted-staggeredtype).

FIG. 10 illustrates a cross-sectional view of an embodiment of a pixelportion and a TFT portion.

FIG. 11 illustrates a cross-sectional view of an alternative embodimentof a pixel portion and a TFT portion.

FIG. 12 illustrates a cross-sectional view of an embodiment of a pixelportion and a TFT portion.

FIG. 13 illustrates a cross-sectional view of an embodiment of a pixelportion and a TFT portion.

FIG. 14 illustrates a schematic diagram of a cross-sectional view of anexperimental sample.

FIG. 15 illustrates a voltage-current characteristic between Cu—Mnelectrodes.

FIG. 16 illustrates a cross-sectional TEM image of the experimentalsample and its XEDS spectra.

FIG. 17 illustrates a schematic diagram of the experimental sample.

FIG. 18 is a cross-sectional view of an embodiment of an interfacialsurface model of the experimental sample.

FIG. 19 is a cross-sectional view of an alternative embodiment of aninterfacial surface model.

FIG. 20 illustrates a cross-sectional view of an embodiment of aterminal electrode structure.

FIG. 21 illustrates a cross-sectional view of an alternative embodimentof a terminal electrode structure.

FIG. 22 illustrates a cross-sectional view of an alternative embodimentof a terminal electrode structure.

FIG. 23 illustrates a cross-sectional view of an alternative embodimentof a terminal electrode structure.

FIG. 24 illustrates a cross-sectional view of an alternative embodimentof a terminal electrode structure.

FIG. 25 illustrates a cross-sectional view of an embodiment of a pixelportion and a TFT portion.

FIG. 26 illustrates the resistance of the copper alloy (Cu—Mn) layer.

FIG. 27 illustrates the resistance of the copper alloy (Cu—Mn) layer.

FIG. 28 illustrates an example of a LCD drive.

FIG. 29 illustrates a propagation delay model of a gate voltage pulseand its related brightness distribution.

FIG. 30 illustrates comparative examples showing adhesive strength oftwo experimental samples.

FIG. 31 is a composition view of an interconnection structure.

FIG. 32 is an enlarged view of a composition of an interconnectionstructure.

FIG. 33 illustrates a cross-sectional view of a TEM image for a Cu—Mnalloy sample.

FIG. 34 illustrates tape test results for evaluating the adhesiveness ofa Cu—Mn alloy sample.

FIG. 35 illustrates resistivity of Cu—Mn layer and the thickness of theoxide layer formed on the Cu—Mn surface.

FIG. 36 illustrates an embodiment of a basic process for manufacturingof TFT devices.

FIG. 37 illustrates an embodiment of a five-mask process formanufacturing of TFT devices.

FIG. 38 illustrates a cross-sectional view of a TFT structuremanufactured with the five-mask process.

FIG. 39 illustrates a cross-sectional view of an electrode terminal foran external connection.

FIG. 40 illustrates a plan view of an embodiment of TFT-LCD moduleshowing pixel and TFT portions.

FIG. 41 illustrates a cross-sectional view of a TEM image for the copperalloy sample after conducting the heat treatment.

FIG. 42 is a composition view of an oxide covering layer of theinterconnections.

FIG. 43 illustrates thickness of an oxide covering layer.

FIG. 44 illustrates a cross-sectional view of an exemplary embodiment ofa gate interconnection structure.

FIG. 45 illustrates a schematic diagram of an organic EL device.

FIG. 46 illustrates a schematic diagram of an equivalent circuit for anorganic EL display device.

FIG. 47 illustrates a cross-sectional view of an embodiment of anorganic EL display device.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present invention will be described hereinafter withreference to the accompanying drawings, in which preferred exemplaryembodiments of the invention are shown. The ensuing description is notintended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the preferred exemplaryembodiments will provide those skilled in the art with an enablingdescription for implementing preferred exemplary embodiments of thedisclosure. It should be noted that this invention may be embodied indifferent forms without departing from the spirit and scope of theinvention as set forth in the appended claims.

Embodiments of the present invention are related to a technique in whichcopper alloy is applied to electrodes and interconnections of amorphoussilicon (a-Si) TFTs forming an active matrix LCD on a TFT substrate.First of all, the liquid crystal display (LCD) device used for thepresent invention will be described.

Referring first to FIG. 1, a cross-sectional view of a thin filmtransistor liquid crystal display (TFT-LCD) module is shown. The TFT-LCDmodule is composed of a LCD display panel 1, a driver circuit 2, abacklight unit 3 and a chassis 4. The LCD display panel 1 consists of aTFT substrate 11 and a color filter (CF) substrate 12, which arepositioned respectively at the lower and upper sides of the LCD displaypanel 1 forming an LCD display cell.

The driver circuit 2 drives the LCD display panel 1 by providingelectrical signals reached from an outside source to the LCD displaypanel 1. The driver circuit 2 may include a LCD driver LSI chip 21, amultilayer printed circuit board (PCB) 22 and a control circuit 23. TheLCD driver LSI chip 21 is electrically coupled with a terminal electrodeof the LCD display panel 1 by an anisotropic conductive film. Inaddition, a lamp 38 and a light guide plate 39 are provided on thebacklight unit 3. The chassis 4 is set to complete the LCD modulestructure.

Referring next to FIG. 2, a cross-sectional view of the LCD displaypanel 1 is shown. As explained above, the LCD display panel 1 includes apair of substrates (TFT substrate 11 and CF substrate 12), arranged toface each other with a gap in which a liquid crystal layer (LC layer) 13is filled. The gap is about 3 to 5 μm, and the distance of the gap iscontrolled by positioning a spacer 14 in the LCD display panel 1. Theliquid crystal layer 13 is liquid, and is sealed by a surrounding seal15. The arrangement of liquid crystal molecules within the liquidcrystal layer 13 controls the rotation of light to direct the polarizedlight as an optical crystal. The liquid crystal molecules alignthemselves with each other, within their physical surrounding, and withan electric field such that they are arranged vertically or transverselyagainst an interface between the liquid crystal layer 13 and the TFTsubstrate 11 or the CF substrate 12. This is called orientation.

As shown in FIG. 2, an orientation film 17 is applied between theinterface of the liquid crystal layer 13 and the TFT substrate 11 or theCF substrate 12. Furthermore, polarizing films 18 and 19 are disposed,respectively, on outer surfaces of the TFT substrate 11 and the CFsubstrate 12. Additionally, a thin film transistor (TFT) 111, a storagecapacity (Cs) 112 and a pixel electrode 113 are placed on an innersurface of the TFT substrate 11 forming a basic TFT-LCD pixel. The LCDdisplay panel 1 includes millions of pixels placed on the TFT substrate11 such that they are connected in form of an active matrix throughinterconnections.

The CF substrate 12, which faces the TFT substrate 11, consists of ablack matrix (BM) 121, a color filter (CF) 122 having three primarycolors (red, green, and blue), and a common electrode 123. In thisembodiment, the common electrode 123 is placed on the CF substrate 12.Other embodiments may use an in-plane switching (IPS) nematic liquidcrystal mode, where the common electrode 123 is placed on the TFTsubstrate 11, as shown in FIG. 3.

Referring back to the FIG. 2, the common electrode 123 is a transparentelectrode, formed from indium tin oxide (ITO), indium zinc oxide (IZO),or indium zinc tin oxide (ITZO). In order to extend the common electrode123 to the TFT substrate 11, a short portion 161 is used between thecommon electrode 123 and the TFT substrate 11 after the surrounding seal15. Each electrode is electrically connected to the driver circuit 2 bya connecting pad 162. In addition, the TFT substrate 11 and the CFsubstrate 12 are required to be optically-transparent, and hard glass isused as a material for them. Incidentally, refer to U.S. Pat. Nos.2,701,698 and 5,598,285 about the IPS nematic liquid crystal mode shownin FIG. 3.

FIGS. 4-6 illustrate respectively a plan view, a cross sectional-view,and a schematic diagram of an equivalent electrical circuit for a pixelportion 31 and a TFT portion 32. Each pixel portion 31 is connected to agate interconnection 33 and a signal interconnection 34. Accordingly, asseen in the plan view of the FIG. 4, the TFT portion 32 has threeelectrodes such as a gate electrode 351, a source electrode 352 and adrain electrode 353. The drain electrode 353 is coupled to the pixelelectrode 113 via a through hole 40.

As shown in FIG. 5, a thin film semiconductor material 36, such asamorphous silicon (a-Si), is disposed between the source electrode 352and the drain electrode 353. The gate electrode 351 is located inproximity to the semiconductor layer 36 but electrically insulatedtherefrom by a gate insulator layer 37. The gate insulator layer 37 ismade of silicon nitride (SiN_(x)) or silicon oxide (SiO_(x)) film. Inother embodiments, the gate insulator layer 37 may be made from alaminated or an organic layer.

As discussed before, the schematic diagram of an equivalent electricalcircuit for each pixel portion 31 is shown in FIG. 6. Parasiticcapacitors C.sub.gs, C.sub.gd, and C.sub.ds are applied respectivelybetween the gate electrode 351 and the source electrode 352, between thegate electrode 351 and the drain electrode 353, and between the drainelectrode 353 and the source electrode 352. In this equivalent circuit,the liquid crystal layer 13, disposed between the common electrode 123of CF substrate 12 and the TFT substrate 11, is represented by C.sub.lc.The storage capacitor C_(s) is connected in parallel to the C.sub.lccapacitor to sustain the pixel electrode voltage during holding period.

FIGS. 7-9 illustrate schematic diagram of alternative embodiments for aTFT structure made of amorphous silicon material (a-Si). By way ofexample, the TFT structure may be a top gate structure having astaggered type, a channel stopper structure having an inverted-staggeredtype, or a channel etch structure having an inverted-staggered type.Among these embodiments, the channel etch structure shown in FIG. 9 isthe most commonly used structure.

[Gate Electrode]

Next, a technique for applying a copper alloy to a gate interconnectionof a TFT electrode will be explained. As described above, the mostcommonly used configuration for TFT structures with amorphous siliconmaterial is the inverted-staggered type with channel etch structure. Inthis embodiment, the gate electrode 351 is deposited on a glasssubstrate 11 by a sputtering method and patterns are formed by wetetching process. Thereby, the gate electrode 351 has a tapered shape inorder to reduce mechanical stress.

In this embodiment, it is preferable to use an alkali-free glass as aglass substrate. Examples of composition for the alkali-free glass areshown below:

Component Content percentage (%) SiO₂ 49.9 Al₂O₃ 11.03 B₂O₃ 15.0 Metal(such as Fe) 25.0 Alkali —

A schematic diagram of a TFT structure using a copper (Cu) alloy as agate electrode is shown in FIGS. 10 and 12. In this embodiment,manganese (Mn), which is an element for forming an alloy with copper(Cu), is used to form the copper (Cu) alloy layer of the gate electrode351. Next, the process of forming an oxide layer over the gate electrode351 is explained.

First, a Cu—Mn layer is deposited on the glass substrate 11 by asputtering method. The thickness of the Cu—Mn alloy layer is about 200nm. Then, a heat treatment is conducted on the glass substrate 11 attemperatures ranging from 200 to 450° C. for about 3 minutes to 50 hoursin an atmosphere containing traces of oxygen. This heat treatmentresults in diffusing manganese (Mn) within the Cu—Mn alloy layer suchthat an oxide layer 47 is formed at the interface between the glasssubstrate 11 and a bottom surface of the Cu—Mn layer. In other words,the bottom surface of the Cu—Mn layer is covered by the oxide layer 47.The thickness of the oxide layer 47 at the interface between the Cu—Mnlayer and the glass substrate 11 is about 2 to 10 nm In fact, manganese(Mn), which is an additional element in copper (Cu) alloy layer,diffuses to the interface with the glass substrate 11 and reacts withsilicon dioxide (SiO₂) forming an oxide layer 47 containing Cu, Mn andSi. This oxide layer may be represented by (Cu, Mn, Si)O_(x). As aresult of this oxide formation, the adhesiveness between the gateelectrode 351 and the glass substrate 11 can be ensured. In addition,the existence of manganese oxide MnO_(x) in the oxide layer 47 mayfurther prevent copper (Cu) from diffusing into the glass substrate 11.

Meanwhile, on the top surface of the Cu—Mn layer, an oxide layer 47containing Cu and Mn, e.g. (Cu, Mn)O_(x), is formed by reaction with theoxygen in the surrounding atmosphere. In other words, the top surface ofthe Cu—Mn layer is covered by the oxide layer 47. Incidentally, thisembodiment shows the structure where the oxide layer 47 sandwiches thegate electrode 351. This is because both the top and bottom surfaces ofthe gate electrode 351 are covered by the oxide layer 47. In the samemanner, an additional heat treatment is conducted on the gate electrode351 at temperatures about 200 to 450° C. in an atmosphere containingtraces of oxygen so that oxide layer 47 is formed on the taperedportions of the gate electrode 351. In other words, the tapered portionsof the gate electrode 351 are covered by the oxide layer 47. The overallthickness of the oxide layer 47 around the gate electrode 47 is about afew nanometer.

Other embodiments may use other methods for forming oxide layer on thegate electrode 351. For example, after forming the gate electrode 351,three layers of SiN/a-Si/n⁺a-Si which represent respectively the gateinsulating layer 37 and semiconductor layers 36 and 45, are successivelydeposited by plasma chemical vapor deposition (CVD) (hereinafter simplyreferred to as “plasma CVD”). During this deposition process, thesubstrate temperature is about 300 to 350° C., which is sufficient forapplying the heat treatment. Thus, when the substrate temperaturearrives to a point around 300 to 350° C., the substrate is placed into aplasma CVD chamber so that the oxide layer 47 can be formed in theatmosphere containing traces of oxygen. Therefore, at the interface withthe glass substrate 11, the oxide layer 47 is formed in the same manneras described before.

Meanwhile, the oxide layer 47, containing Cu, Mn and Si, (Cu, Mn, Si)O_(x), is also formed at the interface between the gate electrode 351and the gate insulating layer 37. This oxide layer 47 can ensure theadhesiveness between the gate electrode 351 and the gate insulatinglayer 37, and further prevent the diffusion of Cu from the gateelectrode 351 into the gate insulating layer 37. In an alternativeembodiment, the gate insulating layer 37 is made of SiON. In thisembodiment, Mn diffuses to the interface of the gate insulating layer 37and reacts with oxygen in SiON and forms the oxide layer 47. The oxidelayer 47 of this embodiment eventually results in an oxide layercontaining Cu, Mn and Si, (Cu, Mn, Si)O_(x), in the same way asdescribed in the previous embodiment.

Since the Cu—Mn layer contains a fixed amount of Mn which diffuses tothe surfaces of the Cu—Mn layer, due to the heat treatment, to form theoxide layer 47, the gate electrode 351 becomes very close to the pureCu. For a heat treatment at temperatures ranging from 200 to 250° C. inthe atmosphere containing traces of oxygen, the resistivity of gateelectrode 351 is about 2.2 μΩcm, whereas the resistivity of bulk pure Cuis about 1.7 μΩcm. The resistivity of resulting gate electrode 351 isadequately lower than the resistivity of Al. Since gate interconnectionsare formed with low resistance gate electrodes 351, the propagationdelay of the gate voltage pulse can be reduced, therefore reducing thenon-uniformity of brightness of LCD due to shadings.

As described above, in this embodiment, the Cu—Mn is applied to the gateelectrode 351, which is sandwiched between the glass substrate 11 andthe gate insulating layer 37, in other words, between different types ofinsulating layers. Then, the oxide layer 47 is formed at the interfaceof insulating layers 11 and 37 covering the gate electrode 351. In thisway, the oxide layer 47 prevents Cu from diffusively intruding into theglass substrate 11 and the gate insulating layer 37 while ensuring theadhesiveness between the gate electrode 351 and the insulating layers 11and 37.

In addition, the formation of the oxide layer 47 covering the gateelectrode 351 results in achieving a low resistivity close to theresistivity of pure copper and therefore reducing the shading ofdisplayed images.

Furthermore, whereas conventional Cu interconnections use threedeposited layers of Cu alloy/pure Cu/Cu alloy, the present embodimentcan use a single deposited layer of copper alloy, e.g. Cu—Mn. Therefore,the present invention is effective in shortening the deposition processand reducing the manufacture cost.

[Source Electrode or Drain Electrode]

With reference to FIGS. 10-13, embodiments of the present invention willbe explained in terms of manufacturing process for applying a copperalloy, e.g. Cu—Mn, to the source electrode 352 or drain electrode 353 ofthe TFT 111 within the TFT-LCD module of the present invention.

A semiconductor layer for the present invention includes, for example,amorphous silicon (a-Si) layer or heavily doped amorphous silicon(n⁺a-Si) layer which contains impurities, and the like.

As explained above, after forming the gate electrode 351, three layersincluding a gate insulating layer 37, e.g. SiN, and two semiconductorlayers 36 and 45 are successively deposited over the gate electrode 351and the TFT substrate 11. Examples of semiconductor composition, used inthe present invention, may include amorphous silicon (a-Si) or heavilydoped amorphous silicon (n⁺a-Si). Then, a dry etch method is used toform a desired pattern on the gate insulating layer 37 and thesemiconductor layers 36 and 45. After the patterning step, a copperalloy layer, e.g. Cu—Mn, is deposited by a sputtering method. Using awet etch process, desired patterns for the source electrode 352 and thedrain electrode 353 are formed. After the patterning step, a heattreatment is applied at temperatures ranging from 200-450° C. and in anatmosphere containing traces of oxygen. Due to this heat treatment, anoxide layer 46 covering the source electrode 352 and the drain electrode353 is formed. Here, the top, bottom and side surfaces of the sourceelectrode 352 and the drain electrode 353 are covered by the oxide layer46. This embodiment also shows the structure where the oxide layer 46sandwiches the source electrode 352 and the drain electrode 353respectively. This is because both the top and bottom surfaces of thesource electrode 352 and the drain electrode 353 are covered by theoxide layer 46. The oxide layer 46 has a thickness of few nm andcontains Cu, Mn, and Si, (Cu, Mn, Si)O_(x), or Cu and Mn, (Cu, Mn)O_(x),depending on which interface the oxide layer 46 is formed. At theinterface where the source electrode 352 or the drain electrode 353 hasa direct contact with the gate insulator layer 37, e.g. SiN, or thesemiconductor layers 36 and 45, e.g. a-Si or n⁺a-Si, the oxygenremaining in the insulating layers 36, 37, and 45 reacts with the Mnfrom the Cu—Mn layer to form the oxide layer 46.

After the heat treatment step, a passivation layer 44 is deposited overthe TFT structure 111 and the gate insulator 37 such that the sourceelectrode 352 and the drain electrode 353 are sandwiched between thepassivation layer 44 and the semiconductor layers 45 or 36. Thisdeposition step is performed at a substrate temperature ranging from250-300° C. by a plasma CVD deposition process. Different embodimentsmay use different composition for the passivation layer 44. Examples ofthose compositions may include silicon nitride (SiN_(x)), silicon oxide(SiO_(x)), silicon nitrogen oxide (SiN_(y)O_(x)), or organic layer, suchas polyimide with a high fluidity. Desired pattern for the passivationlayer 44 is also formed by an etching process. As the deposition processis formed at temperatures ranging from 250-300° C., the oxide layer 46containing Cu, Mn, and Si, (Cu, Mn, Si)O_(x), can be eventually formedat the interface between the passivation layer 44 and the sourceelectrode 352 or the drain electrode 353. This additional oxide layermay have a thickness of a few nm.

In an alternative embodiment, the step of passivation layer depositionmay be performed, directly after the source and drain patterning step,without performing a heat treatment. In this embodiment, Mn in the Cu—Mnlayer diffuses thermally due to a heat generated from the depositionprocess, which is performed at a substrate temperature ranging from250-300° C. Therefore, the oxide layer 46 with a thickness of a few nmis formed around the source electrode 352 or the drain electrode 353, asshown in FIGS. 10-13.

The resulting oxide layer 46 ensures the adhesiveness between the sourceelectrode 352 or the drain electrode 353 with the insulating layers 37or 44, as well as the semiconductor layers 36 or 45. In addition, theoxide layer 46 functions as a high-resistivity conducting layer, suchthat the oxide layer 46 does not become an inhibitor against the ohmiccontact between the semiconductor layer 45, e.g. n⁺a-Si, and the sourceelectrode 352 or the drain electrode 353.

The high-resistivity conducting oxide layer 46 is primarily due to thefact that Cu and Si are also diffusing thermally from the Cu alloy layerand the surrounding semiconductor or insulating layers 36, 37, 44, or 45toward the interfacial oxide layer 46. In addition, using an agingprocess, a voltage within a tens of volts range is applied to the sourceelectrode 352 or the drain electrode 353 so that the insulating propertyof the oxide layer 46 with a few nm thickness breaks down. As a result,the oxide layer 46 functions as a conductive layer ensuring an ohmiccontact between the source or drain electrodes 352 or 353 and thesemiconductor layers 36 or 45.

Furthermore, the source electrode 352 or the drain electrode 353 mayhave low-value resistance, close to the resistance of pure copper, inthe same way described above in regards to the gate electrode 351. Thislow value resistivity of respective electrodes enables the TFT structureof the present invention to reduce the propagation delay and its relateddisadvantages. In addition, depositing a single layer of copper alloy,e.g. Cu—Mn, in the present invention may shorten the deposition process,having an effect of reducing cost compared with the conventional ways.

Different embodiments of TFT structure may result from the manufacturingprocess described above, which are respectively shown in FIGS. 10-13.

Referring next to FIG. 10, a cross-sectional view of an embodiment of aTFT portion 32 and a pixel portion 31 is shown. In this embodiment, thesource electrode 352 and the drain electrode 353 are covered with theoxide layer 46. The semiconductor layer is composed of two layers; anamorphous silicon (a-Si) layer 36 and an amorphous silicon (n⁺a-Si)layer 45 which is doped with an impurity at high concentration. Inaddition, the gate electrode 351 is surrounded by the oxide layer 47.

With reference to FIG. 11, a cross-sectional view of another embodimentof a TFT portion 32 and a pixel portion 31 is shown. This embodimentdiffers from that of FIG. 10 in that the electrode 351 is not surroundedby any oxide layer.

FIG. 12 illustrates a cross-sectional view of an alternative embodimentof a TFT portion 32 and a pixel portion 31. This embodiment differs fromthat of FIG. 12 in that the semiconductor layer is composed of onesingle amorphous silicon layer (a-Si) 36. In addition, the gateelectrode 351 is surrounded by the oxide layer 47.

FIG. 13 illustrates a cross-sectional view of another alternativeembodiment of a TFT portion 32 and a pixel portion 31. In thisembodiment, the semiconductor layer is composed of one single amorphoussilicon layer (a-Si) 36, however the gate electrode 351 is notsurrounded by any oxide layer 47. It has to be noted that similareffects may be obtained in different embodiments of FIGS. 10-13 using amicrocrystal silicon as semiconductor layers 36 and 45. In addition, thepixel electrode 113, common to the different embodiments of FIGS. 10-13,may include, for example, indium tin oxide (ITO), indium zinc oxide(IZO), or indium zinc tin oxide (ITZO), and the like.

The TFT having the above-described embodiments, FIGS. 10-13, may bemanufactured in an alternative process, described as below; First, athin silicon oxide layer SiO_(x) having a thickness of about 1-2 nm isformed on a top surface of the semiconductor layers 36 or 45 (forexample, amorphous silicon (a-Si) or amorphous silicon doped with animpurity at high concentration (n+a-Si)). Different process may be usedto form the silicon oxide layer SiO_(x) of the present invention. By wayof example, an ozone oxidation method or a plasma oxidation method maybe used. According to another embodiment of the present invention, analternative method is provided for forming the silicon oxide layerSiO_(x). The method includes attaching a hydroxy group (—OH) on the topsurface of the semiconductor layer 36 or 45 by spraying moisture vapor.

Then a copper alloy layer, e.g. Cu—Mn, is formed over the silicon oxidelayer SiO.sub.x. After forming the copper alloy layer, a heat treatmentis applied at temperatures ranging from 200-350° C. As a result of thisheat treatment, Mn from the Cu—Mn layer migrates into the silicon oxidelayer, interposed between the semiconductor layer 36 or 45 and thecopper alloy layer, forming an oxide layer 46 containing Mn, Cu, andsilicon, (Mn, Cu, Si)O_(x). The resulting oxide layer 46 may have athickness of a few nm and the main component of the oxide layer 46 isMnO_(x).

(Ohmic Contact)

The resulting oxide layer 46 may have a high-value electrical resistancethat functions as a conductive layer. This conductive layer ensures anohmic contact at the interface between the semiconductor layer 36 or 45and the source electrode 352 or the drain electrode 353. The sourceelectrode 352 or the drain electrode 353 is mainly composed of copper.

Referring next to FIG. 14, a schematic diagram of a cross-sectional viewof an experimental sample is shown. The experimental sample of FIG. 14is manufactured using the process explained in paragraphs [0059-0061].An amorphous silicon semiconductor layer doped with an impurity at highconcentration (n⁺a-Si) is formed on an amorphous silicon (a-Si)semiconductor layer. Then, a silicon dioxide layer (SiO₂) is formed onthe top surface of the n⁺a-Si layer, by using the plasma oxidationprocess. In this embodiment, the thickness of the SiO₂ layer is about1.5 nm. After the oxidation step, a Cu—Mn layer is deposited over theSiO₂ layer and patterned using an etching process in order to obtain twoCu—Mn electrodes. After the patterning step, a heat treatment isconducted at 250° C. for 30 minutes in an atmosphere containing tracesof oxygen. According to this heat treatment, a MnO_(x) layer containingtraces of Cu and Si is formed. The resulting MnO_(x) layer has athickness about 1-2 nm, which surrounds both of the Cu—Mn electrodes.

Also referring to FIG. 14, the a-Si layer gets a process of plasmaoxidation in order to form SiO₂ having thickness in 1.5 nm. CU-4 atm %Mn alloy is deposited. A heat treatment at 250° C. for 30 minutes isconducted in an atmosphere containing a trace of oxygen. A distancebetween pads is 40 nm. A contact resistance is 0.85 cm².

Then, voltage is applied between the two Cu—Mn electrodes of theexperimental sample, to measure the electrical current there between.FIG. 15 illustrates the current-voltage (I-V) characteristic of theexperimental sample. As shown in FIG. 15, the current-voltagecharacteristic between the Cu—Mn electrodes is substantially linearwithin ±10 volts. More particularly, an ohmic contact is obtainedbetween the Cu—Mn electrodes when the applying voltage is within ±5volts. Accordingly, the metal-semiconductor contact, formed between theCu—Mn electrodes and the n⁺a-Si semiconductor layer, represents an ohmiccontact characteristic when the applied voltage between the Cu—Mnelectrodes is within .+−0.10 volts. These results will apply to the TFTstructure of the present invention where the ohmic contact is formedbetween the source or drain electrodes 352 or 353 and the semiconductorlayers 36 or 45.

In the TFT structure of the present invention, it is necessary to obtainan stable connection within pixels of the TFT-LCD module. Therefore, itis desirable to obtain an ohmic contact between the source or drainelectrodes 352 or 353 and their corresponding semiconductor layers 36 or45. In different embodiments of present invention, the source and drainelectrodes 352 and 353 are mainly composed of Cu, which are covered bythe oxide layer 46. The oxide layer 46 is mainly composed of MnOx with ahigh-value electrical resistivity to ensure the realization of ohmiccontacts within the TFT structure.

A cross-sectional TEM image of the experimental sample with its XEDSspectra is shown in FIG. 16. The sample surface (1) shows the formationof a MnO_(x) layer of few nm in average thickness. In addition, theinterface with n⁺a-Si layer shows another MnO_(x) layer of few nm inaverage thickness. The XEDS spectra of FIG. 16 are taken from (1) thesurface layer of the experimental surface, (2) the Cu—Mn inside layer,(3) the MnO_(x) layer formed at the interface with the n⁺a-Si layer, andfrom (4) the n⁺a-Si inside layer.

A weak Si peak is observed in both (1) and (2) spectra. This is mainlydue to the excitation of the Si peak from the dead layer of the XEDSdetector. Thus, a weak Si peak in both spectra should be neglected. Inaddition, the Cu peak in spectra (1) is mainly due to the radiation ofelectron beam in the Cu—Mn layer. Therefore, the Cu peak in spectra (1)should be neglected. The XEDS analysis shown in FIG. 16 (1) confirmsthat the surface layer consists of Mn and O, indicating the formation ofthe upper surface MnO_(x) layer. The spectrum from the Cu—Mn insidelayer in FIG. 16 (2) shows no Si and Mn, indicating that Mn atoms areexpelled from the Cu—Mn layer and the Cu—Mn electrodes of theexperimental sample are mainly made of Cu. FIG. 16 (3) shows Si, Mn, andCu peaks, indicating the formation of a MnO_(x) layer at the interfacewith the n⁺a-Si layer. The spectrum from the n⁺a-Si inside layer in FIG.16 (4) shows only Si peaks, indicating a good diffusion barrier propertyof the MnO_(x) layer at the interface with the n⁺a-Si layer.

Also referring to FIG. 16, depicted is an enlarged picture of a contactportion between CuMn and a semiconductor layer, and a result of analysisof each portion by XEDS. XEDS: X-ray energy-dispersive spectroscopy.Cu-2 atom % mn150 nm/SiO₂1.5 nm/n+/a-Si350° C., 30 nm. Interdiffusion isnot found. Mn mainly exists in the surface. The amount of Mn in theCu—Mn layer and the amount of Mn in the interfacial surface aresubstantially same.

The XEDS spectra of FIG. 16 are taken from (1) the surface layer of theexperimental surface, (2) the Cu—Mn inside layer, (3) the MnO_(x) layerformed at the interface with the n⁺a-Si layer, and from (4) the n⁺a-Siinside layer. In summary, Mn mainly exists in the surface layer of theexperimental sample (1) forming a MnO_(x) layer The amount of Mn in theCu—Mn inside layer (2) and the MnO_(x) layer formed at the interfacewith the n⁺a-Si layer (3) are substantially the same. The MnO_(x) layerat the interface with the n⁺a-Si layer is extremely thin. A schematicdiagram of the experimental sample zoomed at the Cu—Mn electrode withits respective interfaces is shown in FIG. 17.

Referring next to FIG. 18, a cross-sectional view of an interfacialsurface model of the experimental sample is shown. The interfacialsurface model of FIG. 18 is obtained according to the experimentalresults conducted on the experimental sample and explained through FIGS.14-17. As shown in FIG. 18, after depositing a n⁺a-Si layer 6 over thea-Si layer 5, a plasma oxidation method is used to form an extremelythin, e.g. 1-2 nm, SiO_(x) layer 7. Then, the Cu—Mn layer 9 is formed onthe SiO_(x) layer 7. After depositing the Cu—Mn layer 9, a heattreatment is conducted at about 200-350° C. on the stacked layers. As aresult of this heat treatment, oxide layers 8 and 10 are formedrespectively at the interface with the n⁺a-Si layer 6 and the surfacelayer of the Cu—Mn layer 9. The main element of the oxide layer 8 is Mn,but other elements such as Cu and Si are also included in itscomposition. In addition, the oxide 8 may have a thickness of about 2 to3 nm. The oxide layer 10 formed on the top surface of the Cu—Mn layer 9is composed of MnO_(x).

According to the experimental results explained in FIGS. 14-15, an ohmiccontact at the interface between the Cu—Mn layer 9 and the n⁺a-Si layer6 may be realized, despite the existence of the oxide layers 7 and 8with a total thickness of about 5 nm. In other words, generally, in acase where an oxide layer is interposed between a metal layer and asemiconductor layer, there is a possibility that the metal-semiconductorbecomes a Schottky contact or an ohmic contact. However, themetal-semiconductor contact pertaining to the resent invention isconfirmed to be an ohmic contact. Therefore, the source electrode 352and the drain electrode 353 of TFT structures pertaining to the presentinvention may represent the linear current-voltage characteristic of anohmic contact. FIG. 19 illustrates a cross-sectional view of analternative embodiment of an interfacial surface model of theexperimental sample. This embodiment differs from that of FIG. 18 inthat the MnO_(x) layer 8 and the SiO_(x) layer 7 are merged together. AsCu and Si may diffuse from Cu—Mn layer 9 and SiO_(x) layer 7 or n⁺a-Silayer 6 into the MnO_(x) layer 8, the resulting oxide layer 8 may alsocontain Cu and Si.

In what follows a technique for applying the Cu alloy to a terminalelectrode of the LCD display panel 1 will be explained. Referring backto FIG. 1, a terminal electrode is used to connect the LCD display panel1 to the driver circuit 2, via the LCD driver LSI chip 21. In theTFT-LCD module of the present invention, the terminal electrodesassociated with the gate interconnection 33 and the signalinterconnection 34 (see FIG. 4) are made of copper alloy, e.g. Cu—Mn. Aswill be described further below, the terminal electrodes made of copperalloy are covered by an oxide layer formed during manufacturing process.

Different embodiments of terminal electrode structure are shown in FIGS.20-24. In these embodiments, the terminal electrode 66 is covered by anoxide layer 47, which is mainly composed of manganese (MnOx).Additionally, the oxide layer 47 may also include copper (Cu) or silicon(Si) and the like, which makes the terminal electrode 66 more stable inthe atmosphere. With regard to the connectivity with the driver circuit2, since the oxide layer 47 has a thickness of about a few nm,sufficient conductive properties may be obtained through the contactportions by thermo-compression bonding or voltage application.Furthermore, when the oxide layer 47 is formed on the TFT substrate 11,e.g. glass, the terminal electrode 66 may obtain a sufficientadhesiveness with the TFT substrate 11.

With reference to FIG. 20, a cross-sectional view of an embodiment of aterminal electrode 66 is shown. In this embodiment, the layeredstructure on top of the terminal electrode 66 includes three layers: thegate insulating layer 37, the passivation layer 44, and a transparentelectrode 71. The transparent electrode 71 may includes materials suchas indium tin oxide (ITO), indium zinc oxide (IZO), or indium zinc tinoxide (ITZO). The embodiment of FIG. 20 is generally used in order toensure a good environmental resistance. The sufficient conductivityproperty of this embodiment is ensured by applying voltage between thetransparent electrode 71 and the terminal electrode 66.

Incidentally, in a case of manufacturing a TFT structure, as shown inFIG. 25, the existing manufacturing process may be used formanufacturing the terminal of the present invention. Therefore, it ispossible to conduct the same manufacturing process within differentcycles of production without drastically changing the manufacturingprocess. Furthermore, the oxide layer 47 can prevent Cu from intrudinginto the transparent electrode 71 providing a terminal structure with anexcellent environmental resistance.

Referring next to FIG. 21, a cross-sectional view of another embodimentof a terminal electrode 66 is shown. This embodiment differs from thatof FIG. 20 in that the transparent electrode 71 is removed from theterminal electrode structure. In this embodiment, the oxide layer 47 mayhave a thickness about 10 to several tens of nm where the environmentalresistance is still ensured. In addition, the terminal electrode 66 ofthis embodiment is made by a single layer of copper (Cu) alloy material,e.g. Cu—Mn. Further, the electrical connection with ananisotropically-conductive layer may be achieved by a thermo-compressionbonding.

FIG. 22 illustrates a cross-sectional view of an alternative embodimentof a terminal electrode 66. In this embodiment, the passivation layer 44and the transparent electrode 71 are both present in the terminalelectrode structure. However, the gate insulating layer 37 is removed.

With reference to FIG. 23, a cross-sectional view of another alternativeembodiment of a terminal electrode 66 is shown. This embodiment differsfrom that of FIG. 20 in that all three insulating layers including thegate insulating layer 37, the passivation layer 44, and the transparentelectrode 71 are removed from the top surface of the terminal electrode66. Similar to the embodiment of FIG. 21, the environmental resistanceis ensured by the oxide layer 47, which has a thickness about 10 toseveral tens of nm. The sufficient conductive property is obtained bythe thermo-compression bonding. Additionally, the terminal electrode 66is made from a single copper (Cu) alloy layer.

A cross-sectional view of yet another embodiment of a terminal electrode66 is shown in FIG. 24. In this embodiment, the gate insulating layer 37and the transparent electrode 71 are both removed from the terminalelectrode structure.

[Cu Alloy]

In the following paragraphs, an additional element of copper alloy,which is applied to the TFT-LCD module of the present invention, will bedescribed. In various embodiments of the present invention, the copperalloy with its additional element is applied to the gate interconnection33, the signal interconnection 34, the gate electrode 351, the sourceelectrode 352, and the drain electrode 353 of the TFT-LCD module. Theadditional element of copper alloy is a metal element which has an oxideformation free energy, which is negatively greater than the oxideformation free energy for Cu. In addition, the additional element ofcopper alloy has a diffusion coefficient, higher than the self-diffusioncoefficient of copper (Cu).

Since the diffusion coefficient of the additional element is higher thanthe self-diffusion coefficient of copper (Cu), the additional elementmay reach copper (Cu) alloy surfaces faster than other elements.Therefore, an oxide covering layer composed of the additional elementmay be preferably formed on the Cu alloy surfaces.

That is, in a case where the diffusion coefficient of the additionalelement is smaller than the self-diffusion coefficient of copper (Cu), aconsiderable amount of time is needed for the additional element toreach the Cu alloy surfaces. As a result, Cu oxide covering layer suchas CuO, Cu₂₀ and the like is formed on the Cu alloy surfaces.

Since the Cu oxide covering layer does not show a strong barrierproperty, oxygen atoms may intrude into the inside of the copper (Cu)alloy layer forming an oxide composed of the additional element insideof the copper (Cu) alloy layer. In this case, the metal status of copper(Cu) gradually decreases, therefore, the electrical resistance ofinterconnections increases in the TFT-LCD modules.

In order to solve the above mentioned problems, the additional elementof the copper (Cu) alloy layer is chosen, in the present invention, suchthat the additional element has a higher diffusion coefficient comparedto the self-diffusion coefficient of copper (Cu).

Next, the additional element existing in the copper alloy layer of thepresent invention will be described. The additional element of thecopper alloy layer is in a solid solution status and the additionalamount is preferably within the range of 0.1 to 25 atom %. Morepreferably, the additional amount is within the range of 0.5 to 15 atom%. The most preferable additional amount of the additional element inthe copper (Cu) alloy layer is 0.5 to 5 atom %. It has to be noted that,in a case where the additional element of the copper (Cu) alloy layer isnot in a solid solution status, the diffusion of the additional elementwould be difficult. Especially, in a case where the additional elementand the copper (Cu) from the copper (Cu) alloy layer form intermetalliccompounds, the diffusion of the additional element would be very slow.

Furthermore, when the additional element of the Cu alloy layer is lessthan 0.1 atom %, the oxide covering layer will become too thin in orderto prevent the copper (Cu) oxidation process. Meanwhile, the additionalelement of the Cu alloy layer is over 25 atom %, the solid solubilitystatus of the additional element may be separated out at normaltemperatures.

The additional element of the copper (Cu) alloy layer, pertaining to theembodiments of the present invention, is at least one metal elementselected from the group of Mn, Ze, Ga, Li, Ge, Sr, Ag, In, Sn, Ba, Prand Nd. In addition, the additional element of the copper (Cu) alloylayer is at least one metal element, preferably, selected from the groupof Mn, Zn and Ga. Each additional element may be independently used inthe copper (Cu) alloy layer while more than one additional element mayalso be used at the same time. In particular, it is most preferable thatthe additional element of copper (Cu) alloy layer is manganese (Mn). Ithas to be noted that, even though impurities such as S, Se, Te, Pb, Siand the like may get mixed inevitably into the copper (Cu) alloy layer,these impurities are allowed as long as they do not cause anydegradations of different characteristics, such as the electricalconductivity and the tension strength of the copper (Cu) alloy layer.

Embodiments of the present invention are not limited to a specificprocess for forming the copper (Cu) alloy layer. Therefore, platingprocess such as electrolytic plating process or the dissolution platingprocess and the like, may be used to form the copper (Cu) alloy layer.Additionally, physical vapor deposition process such as the vacuumdeposition process, the sputtering process, and the like may also beused. By conducting a heat treatment to the copper (Cu) alloy layer,formed as described above, the oxide covering layer will be formed.

The heat treatment is applied at temperatures ranging from 150 to 400°C., preferably from 150 to 350° C., and more preferably from 150 to 300°C. It has to be noted that, although independent heat treatments arepossible for forming different interconnections of the Cu—Mn layer,these independent heat treatments may preferably be omitted from themanufacturing process. This is mainly because the CVD process isconducted at temperatures ranging from 150 to 400° C. when a passivationlayer 44 is formed on the copper manganese (Cu—Mn) layer. Further, it ispreferable to conduct the CVD process at temperatures ranging from 150to 300° C. At this temperature zone, it is sufficiently possible to formthe copper manganese (Cu—Mn) interconnections while the recent demandsfor decreasing the CVD's temperature process is also met.

The heat treatment is conducted for a time from 2 minutes to 5 hours.When the heat treatment is conducted at a temperature less than about150° C., the formation of the oxide covering layer becomes slow,therefore the productivity of manufacturing line reduces. Meanwhile,when the heat treatment is conducted at a temperature above 450° C., thecopper (Cu) oxidation process for forming the oxide covering layerstarts before the additional element diffuses and reaches the surface ofthe copper (Cu) alloy layer. In addition, in a case where the heattreatment time is applied for less than 2 minutes, the thickness of theoxide covering layer may become too thin. Meanwhile, for a heattreatment applied over 5 hours, the oxide covering layer's formationtime may become too long.

Next, the resistivity reduction of copper manganese (Cu—Mn) layer, whichis the preferable copper (Cu) alloy layer of the present invention, willbe discussed. As described further above, by applying a heat treatment,the copper manganese (Cu—Mn) layer becomes an interconnection orelectrode body mainly made of copper while a manganese oxide (MnO)_(x)layer covers the interconnection or electrode body. FIG. 26 illustratesthe resistance change of the Cu—Mn layer at 350° C. with heat treatmenttime in various atmosphere of Ar plus a ppm level of oxygen.

In order to measure the resistance of the Cu—Mn layer, the oxide layercontaining copper (Cu) and manganese (Mn) is removed from the topsurface of the Cu—Mn layer such that the interconnection body isexposed. Then, the electrical resistance of the copper (Cu)interconnection body is measured. As shown in FIG. 26, the resistancevalue decreases rapidly with heat treatment time in all atmospheres, andis found to almost saturate after 1500 sec. In Ar+50 ppm of oxygen, alow resistivity of 2.2 μΩcm is obtained at 4000 sec. This resistivity isvery close to the resistivity of pure copper (1.7 μΩcm) in bulkmaterial. In this way, an acceptable value for realizing a lowresistivity interconnection body for improving image quality of theTFT-LCD module may be obtained.

The low resistivity of the interconnection body, which is closed to theresistivity of pure copper (Cu), is mainly obtained due to the fact thatthe majority of manganese atoms are expelled from the copper manganese(Cu—Mn) layer by the heat treatment.

Referring next to FIG. 27, the resistance change of the Cu—Mn layer withheat treatment time in Ar atmosphere at 150, 250, 300, 350, and 400° C.is shown. Note that Ar gas contains a trace amount (0.01 ppm) of oxygen.As shown in FIG. 27, the resistivity value of the interconnection bodyis saturated to a low value after about 200 sec for all temperatures.This result means a short process time, which is efficient inmanufacturing the TFT-LCD module of the present invention.

[Shading]

Next, a shading reduction effect, which is one of the main features ofthe present invention, will be explained. The realization of lowresistance interconnections leads to the reduction of the shadingeffect, thereby improving the image quality of the LCD display. First,the operation of a TFT-LCD module with regard to the shading effect willbe described. The LCD display device of the present invention contains alarge number of several pixels positioned in a matrix array (AM-LCD).

As an example, in the case of TFT-LCD modules for digital TVtransmissions, the number of pixels on the LCD display are (1920×3)×1080with a full high definition (HD) configuration. Since one pixel elementis composed of three primary colors (red, green and blue), the number ofpixels across the screen (1920) is multiplied by three, providing atotal number of 5760 pixels or signal lines across the LCD display. Thenumber of rows of pixels or scanning lines down the LCD display is 1080.In the TFT-LCD module of this embodiment, a gate voltage V_(G) isapplied to the gate electrode of the TFT associated with each pixels ofthe LCD display. The value of the gate voltage V_(G) is usually set tobe about 10 to 15V.

Meanwhile, a signal voltage V_(S) is applied to the source electrode ofthe TFT such that the gate electrode pulse functions as scanning signalsor lines. In the case where a frame frequency/rate of the display is setto be 60 Hz, the frame time for displaying each image on the displaywould be 16.7 ms. Meanwhile, where the 1080 scanning lines are scannedby a progressive scanning, the gate electrode pulse width would be setto 16 μs.

As shown in FIG. 28, the pulse period of the gate electrode is about16.7 ms while the pulse width is about 16 μs. Meanwhile, in the casewhere a LCD drive voltage V.sub.lc is set to be about 5V, the signalvoltage Vs applied to the source electrode is to be about 10y, meaningthat the voltage amplitude of Vs is doubled in value in order to drivethe liquid crystal display layer. FIG. 28 illustrates an embodimentshowing a LCD drive waveform in a frame inversion mode. In thisembodiment, the difference between the signal voltage Vs and a commonvoltage V_(com), which is applied to the common electrode 123 of theTFT-LCD module, is defined as a drive voltage for the liquid crystallayer V_(P(t)). The polarity of the drive voltage for the liquid crystallayer V_(P(t)) is reversed at each frame to obtain an alternate current.

In this way, the penetration efficiency of the LCD display creates avoltage modulation on the signal voltage Vs to modulate the brightnessof the LCD display. In addition, during the period when the gate voltagepulse is off the drive voltage for the liquid crystal layer V_(P(t)) isheld. The time period for which the gate voltage pulse is off is about16 ms, which is substantially the same as frame time.

The drive voltage for the liquid crystal layer V_(P(t)) may have twomain status: 1) a write status and 2) a hold status. In addition, thepenetration efficiency of the LCD display depends on effective values ofthe drive voltage for the liquid crystal layer V_(P(t)). Therefore, theLCD drive voltage V_(lc) is defined according to the following formula:

${{\langle{Vc}\rangle}{rms}} = {\frac{1}{2{Tf}}\sqrt{{\int_{t = 0}^{2{Tf}}\left\{ {{{Vp}(t)} - {Vcom}} \right\}^{2}}\ }{t}}$

Wherein the LCD drive voltage V.sub.lc is proportional with the RootMean Square of the drive voltage for the liquid crystal layer V_(P(t)).Here, a switching time of an a-Si TFT drives a capacity load and themobility of the a-Si is small like 0.3 to 1.0 cm₂/V sec. Therefore, theorder of the switching time is μs. Accordingly, during the gate voltagepulse width 16.7 μs, it takes a few μs to turn on the switch of the TFT.

In addition, since the liquid crystal layer 13 functions as a capacityload, it causes some delay in the application of the signal voltage Vs.Thereby, causing some delay in a rising edge of the drive voltage forliquid crystal layer V_(P(t)). Further, in the TFT-LCD module for a TVwith the full HD configuration, 5760 pixels are positioned in one row.The gate voltage pulse is, then, applied to end portions of the gateinterconnections, and a plurality of TFTs which are all positioned inone row become energized simultaneously.

At this point, the gate voltage pulse is propagated from the endportions to the gate electrode of each pixels. The propagation speeddelays when the resistance and the parasitic capacitance of the gateinterconnections increase. This is called propagation delay of the gatevoltage pulse. When the propagation delay increases, sufficient time forwriting the LCD drive voltage V.sub.lc may not be obtained. As a result,it becomes impossible that the LCD drive voltage V.sub.lc for each pixelachieve a predetermined value. For this reason, the penetrationefficiency of the liquid crystal layer becomes uneven. That is, thebrightness of the display becomes uneven, which causes shadings in theLCD display. Surely, such unevenness causes shadings, in the same way asdescribed above, in the in plane switching (IPS) vertically aligned (VA)liquid crystal display devices.

With reference to FIG. 29, a propagation delay model for the gatevoltage pulse and its related brightness distribution is shown. Eachpixel of the gate interconnections may be equivalently represented usinga resistance R and a parasitic capacitance C. The delay of the gatevoltage pulse of RC in each element is accumulated, so that thepropagation delay reaches a few μm at the termination node n5760.

As shown schematically in FIG. 29, the brightness of the LCD displaydevice, which is normally in a white mode, gradually changes along withthe gate interconnections. Therefore, the LCD drive voltage V.sub.lc atthe termination node n5760 does not arrive to a sufficient value, sothat the primary black display may not be shown, but a bright displaywill be shown instead. Accordingly, by decreasing the resistance of thegate interconnection, the propagation delay of the gate voltage pulsewill be reduced. As a result, it is possible to prevent the unevennessof the brightness in the LCD display, thereby preventing the shadingeffect.

In the present invention, as shown in FIG. 29, the shading may bereduced by using the copper interconnections having a low resistancevalue close to resistance value of the pure copper.

Meanwhile, since the number of nodes in the signal interconnections is1080, so the problem related to the propagation delay in the signalinterconnections is not as severe as in the case of the gateinterconnections. However, in accordance with increasing of displaysizes in the LCD panels, the propagation delay in the signalinterconnections may reach a value about 1 to 3·mu·s which is notnegligible. Therefore, reducing the propagation delay is efficient fordecreasing unevenness of the brightness in the LCD display panels. Thismay achieve, according to the embodiments of the present invention, byapplying a copper alloy, in particular Cu—Mn, as an interconnectionmaterials to both the gate and signal interconnections.

[Adhesiveness with Glass]

Next, the adhesiveness between the copper alloy, e.g. Cu—Mn, andinsulating layers, in particular glass, will be explained. As explainedpreviously, thin layer of interconnections and electrodes, formed by thecopper alloy such as Cu—Mn, are covered with oxide layers which areformed by conducting a heat treatment.

In the LCD devices, it is required for the interconnections and theelectrodes to have an excellent adhesiveness with the glass substrateand other insulating layers, present in the LCD structure. Theadhesiveness is generally evaluated by a tape test. Table I shows theadhesiveness, obtained using the tape test results, for three differentmaterials at various temperatures.

TABLE 1 An example of the tape test results for pure Cu and two Cu/Mndouble layered on the insulating layer SiO₂ Heat treatment temperature(° C.) Material (thickness nm) 150° C. 200° C. 250° C. 300° C. 350° C.400° C. 450° C. Cu (150 nm) X X X X X X X Cu (150)/Mn(2) Δ ◯ ◯ ◯ ◯ ◯ ◯laminated layers Cu (150)/Mn(20) Δ ◯ ◯ ◯ ◯ ◯ ◯ laminated layers ◯:excellent adhesiveness X: stripping was observed (adhesiveness isdefective) Δ: partial stripping was observed

For a thin layer of pure copper Cu (150 nm), formed on an insulatinglayer, e.g. SiO₂, some stripping was found and the adhesiveness wasdefective for all temperatures. Meanwhile, in the case of both Cu/Mndouble laminated layers, the heat treatment causes the interdiffusion ofCu and Si at the interface with SiO₂ layer, wherein an oxide layer isformed. The composition formula of the oxide layer isCu_(X)Mn_(Y)Si_(Z)O (0<X<Y, 0<Z<Y). Therefore, an excellent adhesivenesswith the insulating layer SiO₂ may be obtained.

As for the tape test method for evaluating the adhesiveness, a tape wasapplied to a Cu thin layer surface, then a stripping status of the thinCu layer was evaluated when the tape was peeled off. The tape waspressed by nails so as to be adhered onto the Cu thin layer surface andthen the tape was peeled off.

This process was repeated about ten times on the same portion of the Cuthin layer in order to verify whether the Cu thin layer is adhered tothe substrate. Using this process, the results of the tape test methodwere analyzed in detail.

According to these results, in the case of the both Cu/Mn doublelaminated layers, low electrical resistance was shown by conducting heattreatment at temperatures greater than or equal to 200° C. Meanwhile,with regard to the adhesiveness, a partial stripping was observed afterheat treatment at a temperature of about 150° C. When heat treatment wasconducted at 250° C., excellent adhesiveness was observed for variousheating periods. Examples of those heating periods may include 3minutes, 30 minutes, one hour, 20 hours and 100 hours in heating time.Similarly, excellent adhesiveness was observed for heat treatmentconducted at temperatures of about 350° C.

Referring next to FIG. 30, comparative examples illustrating theadhesive strength of two samples at their interface with an insulatinglayer are shown. The first sample used for measuring the adhesivestrength is based on Cu-4 atom % Mn alloy deposited on a SiO₂ substrate(Cu—Mn/SiO₂). A heat treatment is conducted at temperatures of about400° C. for 30 minutes. The second sample is based on a case where Ta,which is often used for semiconductor interconnections, is interposedbetween the pure Cu and the SiO₂ substrate. The adhesive strength ismeasured by a nano-scratch method. In the lateral axis, time forscratching a distance of six micrometers is plotted, which correspondsto scratching speed. The vertical axis is critical normal force at whicha force signal of film delamination was detected, indicating theadhesive strength. It is shown that Cu—Mn/SiO₂ requires a greater forceand, thus, has a higher adhesive strength compared with Cu/Ta/SiO₂ forall scratching speeds.

Referring now to FIGS. 31-32, an example of atomic concentration isshown as a function of distance from the top surface of the Cuinterconnection. According to results from FIGS. 31-32, the oxide layerformed at the interface between the insulating layer SiO₂ and the Cuinterconnections or electrodes is amorphous and has a compositionrepresented by the following formula: Cu_(x)Mn_(y)Si_(z)O. Accordingly,by forming the oxide layer mainly composed of Mn at the interface, theinterdiffusion between the Cu interconnections and the insulating layermay be prevented. In addition, the concentration of Cu and Si changescontinuously across the interface with the interfacial oxide layer.Therefore, it is thought that the excellent adhesiveness may beachieved.

Accordingly, a LCD device and a method for its manufacturing may beprovided. The LCD device can prevent the oxidation of theinterconnection materials by forming oxide covering layers which haveexcellent adhesiveness with semiconductor layers or pixel electrodes. Inaddition, the LCD device may be provided with interconnections,electrodes or terminal electrodes (especially, source electrodes ordrain electrodes) with high conductivity. Further, it is possible toform interconnections and electrodes or terminal electrodes according tovarious embodiments of the present invention, using the actualmanufacturing process while solving simultaneously the above-mentionedproblems.

FIG. 33 shows a cross-sectional view of a TEM image for a Cu—Mn alloysample after a heat treatment is conducted at temperatures of about 250°C. for 10 minutes. The upper portion of the FIG. 33 shows the Cu—Mnalloy layer, while the lower portion shows the glass substrate. At theinterface between both layers, a reaction layer having a uniformcontrast maybe observed. According to the results of the analysis by anX-ray energy dispersive spectrometer (XEDS) attached to the TEM, thereaction layer is an oxide layer mainly composed of Mn. The formation ofthis oxide at the interface of both layers is the main reason forimproving the adhesiveness.

In order to reduce the resistance of the oxide layer, it is mostlypreferable to add Mn in efficient quantities. For example, in a casewhere a heat treatment is conducted at temperatures of about 250° C. for10 minutes to an alloy layer having a thickness of about 200 nm, aninterface oxide layer having a thickness of about 6 nm is formed. Theamount of Mn contained in the interfacial oxide layer is about 50%. Thisis equivalent to the existence of pure Mn having a thickness of about 3nm. Therefore, the amount of Mn added to the alloy layer is about 3/200in volume ratio. In light of the concentrations of Cu and Mn, Cu-(1 to2) atom % Mn is the most preferable. When the alloy layer has athickness of about 100 nm, the concentration of Mn should be twice theconcentration of Mn when the alloy layer has a thickness of about 200nm. On the other hand, when the alloy layer has a thickness of about 300nm, the concentration of Mn should be 2/3 times of the amount when thealloy layer has a thickness of about 200 nm.

In the present embodiment, Cu-4 atom % Mn alloy is deposited on theglass substrate using a sputtering method. Then, a heat treatment isconducted at temperatures ranging from 150 to 350° C. in a pure argonatmosphere for a period of about 10 to 60 minutes. Next, scotch tapeswere adhered to the alloy thin layer surfaces of both samples, where oneof which is subjected to the heat treatment after the deposition steps,and the other is not subjected to the heat treatment. By peeling thetape from the surface, it is evaluated whether the thin layer isstripped or not (Tape test). As a result, the alloy thin layer in whichthe heat treatment was not conducted is stripped off from the glasssubstrate.

Referring next to FIG. 34, tape test results for evaluating theadhesiveness of a Cu—Mn alloy after depositing on a glass substrate andconducting a heat treatment at various temperatures and heating periodare shown. In this figure, X indicates a case where the stripping wasobserved, A indicates a case where the stripping was sometimes observed,and O indicates a case where the stripping was not at all observed.Incidentally, the stripping was observed for all conditions (temperatureand time) when a pure Cu layer was used. It has to be noted that, inthis embodiment, no stripping was observed when the heat treatment wasconducted at temperatures of equal or greater than 250° C. for allheating period. Meanwhile, as shown in FIG. 34, when the heat treatmentsis conducted at temperatures of about 200° C. for not less than 20minutes or is conducted at temperatures not less than 250° C. for notless than 10 minutes, the alloy thin layers are adhered to the glasssubstrate. When the same tape test is conducted with a pure thin Culayer, stripping is observed for all heat treatment conditions.Accordingly, it was turned out that an excellent adhesiveness againstthe glass substrates may be achieved by conducting a heat treatment atnot less than 200° C. with the Cu—Mn alloy sample.

Incidentally, when Cu alloy contains Mn in an excessive amount, which ismore than the amount needed to form the interfacial oxide layer, theheat treatment should be conducted in a highly-pure Ar gas (the oxygenconcentration is not more than 0.1 ppm) containing oxygen as aninevitable impurities. With reference to FIG. 35, measurement resultsrepresenting resistivity of a Cu—Mn layer and thickness of the oxidelayer formed on the Cu—Mn surface are shown. It has to be noted thatthese measurements were taken after conducting a heat treatment at atemperature of about 350° C. to the Cu—Mn layer. As shown in FIG. 35, Mnleft in the Cu—Mn alloy layer after forming the interfacial oxide layerreacts with oxygen, which is not more than 0.1 ppm in the pure Ar, andforms oxide on the surface thereby being enabled to get out of the Cu—Mnalloy layer. According to the results shown in FIG. 35, the resistanceof Cu—Mn layer may decrease in accordance with the growth of Mn oxidelayer on the surface. The resistance after 30 minutes heat treatment maydecrease to a value, which is almost equal to the resistance value ofpure Cu. According to the results taken by XEDS, Mn concentration wasnot detected in the alloy layer. Accordingly, in this embodiment, theexcess amount of Mn from the Cu—Mn alloy layer can be completelyeliminated by forming the Mn oxide layer on its surface.

[Manufacturing Process]

With regard to the liquid crystal display (LCD) devices of the presentinvention, manufacturing process for forming the oxide layers relatingto copper alloy and their interconnections will be explained. The copperalloy is used as interconnection materials and electrode materials forTFT-LCD devices.

FIG. 36 illustrates an embodiment of a basic process for manufacturingof TFT devices. First, a thin layer 51, which consists of a metal, asemiconductor and an insulator layers, is formed. Then, the thin layer51 is patterned, by photolithography and etching methods, using a photomask 52 and a resist 53. A sputtering method is used for depositing themetal layer, while a Chemical Vapor Deposition (CVD) is used fordepositing the semiconductor and the insulating layers. Examples ofetching methods may include a dry etching method or a wet etchingmethod. The wet etching is generally used for metals which are used ininterconnections. The etching process is repeated four to five times formanufacturing TFTs.

Referring next to FIG. 37, an embodiment of a five mask processes formanufacturing of TFT devices is shown. The order of manufacturingprocess is given as follows: (1) mask 1; patterning the gate by a wetetching method, (2) mask 2; three layers of SiN/a-Si/n⁺a-Si areprocessed altogether using a dry etching method, (3) mask 3; patterningthe source/drain electrodes using a wet etching method, (4) mask 3; adry etching method is conducted to an amorphous silicon (n⁺a-Si)containing impurities so as to form a channel structure, (5) mask 4;patterning a SiN layer, which is a passivation layer (protective layer),(6) mask 5; patterning the Indium Tin Oxide (ITO) layer, which is atransparent electrode. Accordingly, a TFT structure is manufactured.

FIG. 38 illustrates a cross-sectional view of the TFT structuremanufactured with the five-mask process. As shown in FIG. 39, in thegate terminal portion, which is an external electrode, laminatedstructures are formed using a metal and an ITO layers. FIG. 40illustrates a plan-view of TFT-LCD module showing pixel portions and TFTportions.

The additional element in the copper alloy layer, pertaining to thepresent invention, has an oxide formation free energy which isnegatively greater than the oxide formation free energy for an elementin an oxide layer. Accordingly, an oxide covering layer can be formed byreducing the oxide described above. Further, in an oxidation atmosphere,an oxide covering layer may be formed without reducing the oxide.

The Cu alloy, used as the interconnection and electrode materials of theTFT-LCD module of the present invention, is in contact with aninsulating layer containing oxygen. As a result, the additional elementof Cu alloy diffuses toward the interface and the additional element isoxidized so as to form the interface oxide layer.

Further, each of the elements contained in the insulating layer, Cu, andthe additional element in the Cu alloy layer, respectively, forms anoxide so as to form a composite oxide layer. For example, in a casewhere the TFT substrate contains an oxide such as SiO₂ and the like, thegate interconnections of the Cu alloy are formed on the substrate andthen a heat treatment is conducted. As a result, the additional elementin the Cu alloy forming the gate interconnections diffuses into theinterface between the substrate and the gate interconnections, and thenreacts with oxygen in the substrate. Accordingly, an oxide interfacelayer is formed.

In addition, for example, on the gate electrode 351, the gate insulatinglayer 37, composed of SiNO and the like, is formed. By conducting a heattreatment during the manufacturing process, an oxide layer containingCu, Si, and the additional element, (Ci, Si, the additionalelement)O_(x), is formed at the interface between the gate electrode 351and the gate insulating layer 37. Accordingly, the oxide layer is formedon the surface by using the copper alloy as the interconnection andelectrode materials of the TFT-LCD devices.

Now, the manufacturing process for the LCD device of the presentinvention will be provided. Using a physical vapor deposition (PVD)method or a chemical vapor deposition (CVD) method, a Cu alloy layer isdeposited on the TFT substrate 11. The Cu alloy layer is mainly composedof Cu and an additional element used for forming an oxide layer on itssurface and at the interface with the substrate. Then, aphotolithography and etching methods are used for patterning the copperalloy layer, so as to form at least one of the interconnections andelectrodes.

In this embodiment, the additional element of the copper alloy layer, isa metal element preferably selected from the group of Mn, Zn, Ga, Li,Ge, Sr, Ag, In, Sn, Ba, Pr, and Nd. In addition, in this embodiment,manufacturing process is performed such that an oxide layer is formed onat least one surface of the obtained interconnections or electrodes.

It is preferable that the atmosphere gas, used for the process offorming the oxide layer, is an inert gas such as argon which containsoxygen in the amount of not less than 0.01 ppm and not more than 100ppm. In addition, the oxygen concentration in the atmosphere gas ispreferably 5 to 50 ppm. Alternatively, an argon gas which containsoxygen as inevitable impurities may be used. Further, after forming atleast one of either the interconnections or electrodes, a heat treatmentis conducted at temperatures ranging from 150 to 400° C. for a periodranging from 2 to 50 hours. Thereby, an oxide layer of the additionalelement in the copper alloy layer may be formed on the surface of atleast one of the interconnections or the electrodes.

In this embodiment, Cu-2 atom % Mn alloy, which is composed of Cu having99.9999% purity and Mn having 99.98 purity, is used as a targetmaterial. After a thin layer of the alloy is deposited on an insulatinglayer SiO₂, the heat treatment at a temperature of not less than 150° C.and not more than 450° C. is conducted, thereby forming a sample foranalysis. Then, the composition of the thin layer is analyzed, using anAuger electron spectroscopy, from its surface to its depth direction.

FIG. 41 illustrates a cross-sectional view of a TEM image for the copperalloy sample after conducting the heat treatment. By using atransmission electron microscope and an electron energy lossspectrometer (EELS), the microstructure observation and compositionanalysis are conducted. An example of the results is shown in FIG. 42.Stable oxide layers are formed at the interface between the Cu—Mn alloylayer and the insulating substrate layer as well at the Cu—Mn alloysurface. The oxide layers are mainly composed of Mn and their thicknessis about few to twenty-some nm.

FIG. 43, illustrates the thickness of oxide layer as a function of theheating period. Table II summarizes the thicknesses of the obtainedoxide layers for various Mn atom concentration, heating time period, andtemperatures. Referring back to FIGS. 31-32, the atomic concentration ofCu—Mn sample is shown as a function of distance. According to theseresults, Mn shows a distribution where its peak is substantially at thecenter of the oxide layer. It should be understood that even though Cuintrudes into the oxide layer from the interconnection body side, theintrusion of Cu into the insulating layer is prevented.

TABLE 11 The thicknesses of formed oxide layers Atom concentration inCu-Mn alloy Heat treatment Heat treatment temperature (° C.) (at %) time(minutes) 350° C. 450° C. 10% 20 minutes 3.2 nm 6.1 nm 20% 30 minutes8.2 nm

A requisite relating to a sputtering target is provided, in the casewhere Cu—Mn is used as the copper alloy in the LCD device of the presentinvention. More specifically, in the TFT-LCD module of the presentinvention, the propagation delay in the gate interconnection increases.As described above, in order to reduce this propagation delay, it ispreferable to use copper interconnections to achieve low resistivityinterconnections, which is close to the resistivity of the pure copper.

FIG. 44 illustrates a cross-sectional view of an exemplary gateinterconnection using Cu—Mn. The gate interconnection is composed of aninterconnection body 171 and an oxide covering layer 172. Parameters a,b, h, t₁ and t₂, shown in FIG. 44, indicate the size of each portionrelated to the gate interconnection. The sizes of a and b are in therange of a few to ten-some μm. The size of h is around 200 to 500 nm.The sizes of t₁ and t₂ are around 2 to 10 nm. In order to realize aninterconnection body 171 with a resistance close to the resistance ofthe pure copper, it is preferable that the corresponding amount of Mncontained in the covering oxide layer 172 after the heat treatment,being the same amount contained in the Cu—Mn alloy layer before the heattreatment. Accordingly, the amount of Mn, which is the additionalelement in the target of the sputtering method, is defined.

[Organic EL]

The present invention is not limited to the TFT-type liquid crystaldisplay device. The present invention may also be applied to organic ELdisplay devices. FIG. 45 illustrates a schematic diagram of one exampleof the organic EL device according to the present invention. The organicEL device mainly includes a glass substrate 201, an anode (ITO) 202, ahole transporting layer (HTL) 203, an emitting layer (EML) 204, anelectron transporting layer (ETL) 205, and a cathode 206 positioned onthe electron transporting layer 205 sequentially laminated on the glasssubstrate 201. As the emitting layer, for example, organic substancessuch as diamines and the like are used. The anode 202 and the cathode206 are electrically connected through a power source by an electrodewire. Each layer has thickness of, for example, about tens of nm.

With reference to FIG. 46, a schematic diagram of an equivalent circuitfor an organic EL display device is shown. The organic EL display deviceincludes a scan line 194, a signal line 195 and a power line 196 whichcross in the matrix way on a substrate 201. There is a pixel region 198surrounded by the scan line 194, the signal line 195 and the power line196. In this embodiment, the pixel region 198 includes an organic ELelement 191, a drive TFT 192 and a switch TFT 193.

The organic EL includes an anode, a hole transporting layer, an organicemitting layer, an electron transporting layer and a cathode, which arelaminated on a glass substrate. One pixel is composed of a TFT circuitand an organic EL element. A plurality of pixels are positioned in thematrix way. This is called an active matrix organic EL display device.

FIG. 47 illustrates a cross-sectional view of an organic EL displaydevice. The organic EL display device may include a driving TFT portion182 and an organic EL element 184, which are positioned on the glasssubstrate 181. In addition, a TFT electrode 183, a cathode 185 made frommetals, and a transparent electrode 186 is included. In this embodiment,light 187 is emitted toward a lower portion of the substrate.

In the active matrix type organic EL display device, there exists aproblem with regard to the unevenness of picture images. The unevennessis caused by the propagation delay of the gate voltage pulse occurred inthe active matrix type liquid crystal display device. In order to solvethe problem, copper alloy is used as an interconnection material havinghigh conductivity.

The copper alloy in the present invention is used for the scan lines andthe signal lines. In the organic EL display device according to thepresent invention, at least one of the scan line, the signal line, thepower line and the electrode of the TFT is formed from the copper alloymainly composed of copper. The copper alloy is to form oxide layers ofthe additional element that is added to the copper. The oxide layercovers interconnections or electrodes. The structure of cross-sectionalview of the interconnections is illustrated in FIG. 44.

Furthermore, the copper alloy of the present invention is a copper alloyin which the additional element diffuses in the surface of the copperalloy and oxide covering layers of the additional element are formed. Inaddition, the additional element may be at least one metal elementselected from the group of Mn, Zn, Ga, Li, Ge, Sr, Ag, In, Sn, Ba, Prand Nd. More preferably, the additional element may be at least onemetal element selected from the group of Mn, Zn and Ga. In addition, itis the most preferable that the additional element is Mn.

Furthermore, it is preferable that the electrode terminal for anexternal connection has a structure according to the structure shown inFIGS. 20-24.

1. A liquid crystal display (LCD) device having a thin film transistor(TFT), the TFT comprising: a source electrode; a drain electrode, whereat least one of said source electrode and drain electrode comprises: afirst layer comprising copper, a second layer forming an oxide layer andcovering said first layer; and a semiconductor layer having asubstantially linear current voltage relationship with said sourceelectrode or drain electrode including said first and second layers,when a voltage is applied between the semiconductor layer and saidsource electrode or drain electrode.